Signaling system



Aug. 28; 1934.. L. A. I -IYLAND 7 7 SIGNALING SYSTEM Filed April 24, 1931 2 Sheets-Sheet l INVENTOR LawrerzwA/Syland.

' BWQM ATTORNEY L. A. HYLAND 1,971,347

SIGNALING SYSTEM Aug. 28, 1934.

Filed April 24, 1931 2 Sheets-5heet 2 Jig. 4.

llllll J v v INVENTOR a LawrezzceA/fylmzd.

ATTORNEY l sible.

Patented Aug. 28, 1934 PATET OFICE 1,971,347 SIGNALING SYSTEM Lawrence A. Hyland, Washington, D. 0., assigno'r to Eclipse Aviation Corporation, East Orange, N. J., a corporation of New Jersey Application April 24, 1931, Serial No. 532,496

8 Claims.

(Granted under the act of March 3,1883, as amended April 30, 1928; 370 0. G. 757) The present invention relates to signaling systems and more particularly to systems of the regenerative type.

One of the objects of the invention is to provide a novel method of operating a regenerative signaling system, and apparatus for carrying out the method whereby so-called super-regenerative action or amplification is obtained in a more efficient manner than has heretofore been pos- The novel methodof the invention comprises impressing the varying potentials of the current to be amplified upon a regenerative circuit or system embodying an electron discharge device l6 and adjusted to, a critical point at which the circuit tends to oscillate very strongly, and periodically varying the internal or output impedance of the electron discharge device at some frequency which may be relatively low as compared to the frequency of the current to be amplified so as to periodically start and stop the oscillations in the circuit whereby super-regenerative action or amplification is obtained.

As is well known in the art, in the usual form of a circuit employing aregenerative or feedback principle, the regenerative amplification continually increases as the feed-back coupling is increased, i. e., as the amplified oscillation is utilized more and more to reinforce the impressed 0 oscillation until the point is reached where the electron discharge device begins to oscillate and generates sustained oscillations, i. e., the point where the regenerative effect is strong enough to automatically build up an oscillation and sustain it indefinitely by the energy derived from the local source, the regenerative amplification becomes a maximum either atthis point orat a point slightly above or below it, depending on the initial strength of the signal, the characteristics of the electron discharge device, and circuits associated therewith. In general, there is in practice no great difference in the amount of regenerative amplification obtained at any of these three points of adjustment and the amplification so obtained may be considered as the limited value of simple regenerative amplification.

It has heretofore been the practice to obtain super-regenerative action by adjusting a regenerative system to its maximum sensitiveness, i. e., to or near the oscillating condition, and then periodically varying the relation between the amount of feed-back action and the damping of the system. It has been found, however, that such regenerative action of amplification may be to another, is substantially eliminated or preobtained more eificiently and effectively than has heretofore been possible, by a novel and improved method which consists in starting and stopping the sustained oscillations produced by the regenerative action by periodically varying the internal or output impedance of the electron discharge device employed in the system. By this novel method inter-action and disturbing oscillations between associated circuits arereduced to a minimum or are substantially eliminated.

The periodical variation of the internal or output impedance of the electron discharge device may be accomplished, for example, by intrposing an auxiliary electrode between said input and output electrodes and causing the conductance of said auxiliary electrode to periodically vary by impressing thereon an alternating potential derived'irom a local source of oscillations as, for example, a vacuum tube oscillator. This latter will be referred to hereinafter as a variation oscillator. The frequency of this variation oscillator may be sub-audible, audible or super-audible, depending upon the purpose for which the signaling system is to be employed.

Therefore, another object of the invention is to provide a novel and improved method of obtaining super-regenerative action whereby electron discharge devices of the four-electrode type as, for example, the so-called screen-grid type, may be employed.

Another object is to provide a novel circuit arrangement for a signaling system or" the superregenerative type wherein a loss of radio fre-, quency energy, due to leakage from one circuit vented.

A further object is to provide a novel superregenerative signaling system embodying a regenerative circuit including a four-electrode electron discharge device, means for impressing an alternating potential on the auxiliary electrode of the discharge device for varying the output impedance of the latter, and means for maintaining said auxiliary electrode at a normally, low positive potential so that the degree of variation of the alternating potential may be kept within the desired limits required for the most efficient operation of the electron discharge device.

Another object of the invention is to provide a novel circuit arrangement for a signaling sysdischarge device to obtain super-regenerative action without producing an undesirable audio hum which is generally present in a system of this type when the electron discharge device is made to oscillate too strongly, or when the impressed alternating potential is too great. 7

Still another object is to provide in a signaling system, the combination of a regenerative amplifier circuit embodying a four-electrode electron discharge device, a detector circuit coupled thereto, and a novel circuit arrangement including means whereby the signaling system may be converted either to a super-regenerative type or to a straight tuned radio frequency type without super-regenerative amplification.

Other objects and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawings, wherein are illustrated several embodiments of the invention. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not designed as a definition of the limits of the invention, reference being had for this purpose to the appended claims.

In the drawings, wherein like reference characters refer to like elements throughout the several embodiments,

Fig. 1 shows a simple feed-back or regenerative circuit embodying the novel arrangement of the invention for producing periodical variation of the internal impedance of the electron discharge device; 7 V

Fig. 2 illustrates a system similar to that of Fig. 1 with a bias voltage applied to the auxiliary electrode of the electron discharge device;

Fig. 3 illustrates another embodiment wherein a separate electron discharge device is employed as a detector;

Fig. 4 is another embodiment wherein a regenerative detector is employed in addition to the super-regenerative circuit embodying the invention; and

Fig. 5 is a further embodiment of a signaling system of the invention wherein the amplification system may be converted to either a superregenerative type or to a simple tuned radio frequency type.

Referring now to the drawings and more particularly to Fig. 1, there is illustrated a simple inductively coupled regenerative or feed-back circuit wherein a single electron discharge device is employed as a combined radio frequency amplifier and detector. It is obvious that a capacitively coupled feed-back may be employed without departing from the scope of the invention.

Reference numeral 6 represents the input coil or antenna coupling coil which is connected to an antenna collector 7 and a, ground or counterpoise 8, The antenna coil 6 is inductively coupled to the inductance coil '9, the latter which, together with the variable capacity 16 connected in parallel therewith, forms the tuned input or grid circuit of the electron discharge device or vacuum tube 11; the latter, for the purpose of the present invention, as will appear more fully hereinafter, being of the four-electrode type generally known as the screen-grid tube. The control electrode of the tube is shown at 12, the cathode, or filament at 13, the auxiliary electrode at 14 and the anode or plate at 15. A source of potential 16 is connected between the control electrode and filament for providing a suitable negative bias on said control electrode so that the electron discharge device may be employed as a combined amplifier and detector, as is well known in the art.

The filament 13 is heated from a suitable source of electrical energy 17 and the potential across the filament may be adjusted to a desired value by a suitable resistance or rheostat 18. The output or plate circuit of the discharge device is completed through a feed-back or tickler coil 19, a sound reproducing device, as for example a pair of telephones 20 which are by-passed by a suitable condenser 21, and thence through a source of suitable positive plate potential or current 22 to the filament return. The feed-back or tickler coil 19 is placed in proper inductive and phase relation to the inductance coil 9 so that regenerative action takes place, and the coupling between the coils 19 and 9 is made variable so that the circuit may be adjusted to, above, or below the point of oscillation.

A novel method is now provided for periodically starting and stopping the oscillations in the circuit whereby super-regenerative action or ampli fication is obtained and consists, broadly, in periodically varying the internal impedance of the electron discharge device, and more specifically, consists in impressing an alternating potential on the auxiliary electrode 14 whereby the con ductance of the latter is periodically varied, since it becomes alternately positive and negative with respect to its average potential.

For the purpose of carrying out this method, a

novel circuit arrangement is provided which, in H the form shown, consists in coupling the auxiliary electrode 14 to a suitable local source of oscillations, as for example, a vacuum tube oscillator tuned to a frequency preferably below that of the incoming frequency which is impressed on the input circuit of the electron discharge device 11, as hereinbefore stated. To this end the auxiliary electrode 14 is connected through a coupling coil 23 to the filament or cathode l3. Coil 23 is inductively coupled to an inductance coil 24, the latter which, together with a capacity 25, forms the tuned grid circuit of the variation oscillator, the vacuum tube 26 of which is of the tln-ee-eleotrode type having a control electrode or rid 27, a cathode or filament 28 and an anode or plate 29. The anode 29 is connected through a feed-back coil 30 which is inductively coupled to inductance coil 24 in such a manner that free oscillations are sustained in the circuit and the anode circuit is then completed through the source 22 the rheostat 18 to the filament 28.

It will be apparent that when the variation oscillator is functioning to generate continuous oscillations, the potential and current induced in the auxiliary electrode end of the coil 23 from the coil 24 will alternately be positive and negative and hence the potentials impressed on the auxiliary electrode 14 will alternately be positive and negative with respect to its average potential. It will also be apparent that since the regenerative circuit embodying the electron discharge device 11 is adjusted to a critical point at which it would normally tend to oscillate, the introduction of a more positive potential on the auxiliary electrode l i'will cause the circuit negative resistance to reach a value where free oscillations may be triglet becomes impossible for freeoscillations to be genr erated regardless of whether or not the incoming signal voltage is avail'ableto trigger off the circuit. The specific action of the changing of the potential on the auxiliary electrode is to decrease the output impedance of the electron discharge device when a higher positive potential is applied, and to increase the output impedance of said device when a higher negative potential is applied to the auxiliary electrode. Therefore, the

condition is obtained where the auxiliary electrode is alternately positive and negative with respect to its average value, thereby periodically increasing and decreasing the conductance thereof, which in turn alternately decreases and increases the impedance of the anode or output circuit of the electron discharge device. Hence, the circuit will be in a condition where free oscillations can be triggered olf readily by a signal, during the period when the auxiliary electrode is positive; but conversely, the triggering-of free oscillations will be prevented when the auxiliary electrode has a potential thereon which is negative with respect to its average potential. This is the condition essential for super-regenerative action or amplification and the signaling system thus illustrated and described is of a super-regenerative type in which the four-electrode electron discharge device is acting as a super-regenerative amplifier 'detector, while the three-electrode electron discharge device is functioning as the variation oscillator.

In order to prevent or substantially eliminate frequency choke coil 31 which offers a relatively high impedance to. currents which are within the frequency range at which the signaling system is to be employed, i. e., within the frequency range of the tuned circuit 9-,l0, but of relatively low impedance to the alternating potentials which are impressed on the auxiliary electrode 14.

Referring to Fig. 2, there isiIlustrated another novel circuit arrangement embodying the present invention, whichissimilar to that shown in Fig. 1 with the exception that the coupling coil 23, by which the variation oscillator is coupled to the screen-grid,,does not return directly to the filament on the lowpotential side, but is connected to a suitable source of biasing potential 32. The function of this biasing potential is tokeep the screen-grid at a normallylow positive poten- :.i tial so that the degree of variation of the alternating potential supplied by the ,variationoscillator, may be kept within the limits required for the most efficient-operation of asuper-regenerative electron discharge device. Separate sources of potential 33 and 34 are also provided for the filament and plate respectively of the electron discharge tube of the oscillator.

In Fig. 3 there is disclosed still another novel circuit arrangement of a signaling system emr bodying the present invention, which has several advantages over the circuits shown in Figs. 1 and 2. It is well known that one of the difi'iculties met with in the employment of a super-regenerative system where the variation oscillator supplies an audible frequency, is the characteristic audio humwhich is generally present when the superregenerative tube ismade to oscillate too strongly, or when the variation oscillator supplies an excessive amount of energy. ,There is also a 3 residual audio note which is present at all times due to the audible frequency generated by the oscillator, and interferes with the reception of veryweak signals. Therefore, the novel circuit arrangement shown in Fig. 3 provides a signaling system-wherein the above mentioned disturbing effects are largely reduced or substantially eliminated. In this embodimenathe super-regenerative electron discharge deviceis employed entirely as a radio frequency amplifier and a separate detector circuit is provided for rectifying and translating the amplified currents into sound vibrations. For this purpose, the'output or 'plate circuit of the super-regenerative tube 11, instead of being completed directly through a sound reproducing device, is completed through an untuned coil 33 which is closely coupled to an inductance coil 34 which, together withthe variable condenser 35, comprises the tuned input or grid stantially eliminated or prevented. The output or plate circuit of this tube is completed through the sound reproducing device 20 which is bypassed by the condenser 2 l, and through a suitable source of plate potential 40 to the filament return. A suitable negative bias is impressed on the grid 37 from a source 41 so that the tube operates as a rectifier and a separate source of potential 42 is provided for the filament 38. It will thus be seen that'the audio frequency of the variation oscillator, which is impressed on the super-regenerative electron discharge device, cannot reach the rectifying device or detector tube 36 through the coupling between coils 33 and 34 when no incoming signal is present, 1. e., audio frequency impulses cannot reach the grid 37 due to the fact that the coefiicient of coupling between coils 33 and 34 is extremely low for audio frequencies. If, however, there is an incoming radio frequency signal present, this signal, after super-regenerative amplification, will be present in coil 33 in the form of a series of wave trains composed of radio frequency energy varying at an audible rate. Due to the radio frequencycomponent, these wave trains will be transferred efliciently to coil 34 and thence impressed on the grid 37 of the detector tube. The result thus embodying the present invention is shown in Fig.

4 which issimilar to 'thatof Fig. 3 except that a regenerative detector is employed which makes possible the additional amplification of received signal voltages aswell asimproving the selectivity of the system, and for this purpose the output or plate circuit of the rectifying device or detector tube 36 is completed through a feedback or tickler coil 43 which is variably coupled to the inductance coil 34 of the tuned'input circuitof the detector tube.

In Fig. 5 there is illustrated a still further embodiment of a signaling system embodying the present invention, wherein the system may be converted from a super-regenerative type to a straight tuned radio frequency type. For this purpose .there is provided a three-pole doublethrow switch i4 in which the movable elements are blades 45, 46, and g? which are arranged to be thrownto the left or to the right so that they contact with either contacts 48, 49, and or with contacts 51, 52, and 53 respectively, When the switch 44 is thrown to the left, as viewed in the figure, the circuit arrangement is then identical with that shown in Fig. 4 in which the fourelectrode electron discharge device is employed as a super-regenerative amplifier coupled to a regenerative detector. If, however, the switch is thrown to the right, the circuit arrangement then is that of a straight tuned radio frequency amplifier and regenerative etector. In the latter case, the auxiliary electrode or screen-grid instead of being employed to start and stop the oscillation of the super-regenerative circuit, is now placed at ground potential through a suitable condenser 54 and is supplied with normal screen-grid potential through contact 55 which is connected to the source 22.

As pointed out hereinbefore, the variation oscillator employed in any one or all of the illustrated embodiments may be tuned togenerate alternating potentials which may be either at sub-audible, audible, or super-audible frequencies, depending on whether spark, key-modulated, voice-modulated, or pure continuous waves areto be amplified. 1

The method of adjustment of the superregenerative circuits is as follows:

Initially, the variation oscillator is preferably temporarily out out and the tuned circuit 9-10 is adjusted to the desired frequency for the-reception of incoming signals at that frequency. The coupling between'the tickler coil 19 and thev inductance coil 9 is then adjusted, as in the ordinary regenerative circuit, until the system is at the point of oscillation. The variation oscillator is then rendered operative so that the alternating potentials are impressed on the auxiliary electrode 14. The input circuit 9-10 is then retuned and the coupling between the tickler coil 19 and the inductance coil 9 readjusted. As these readjustments are made, a point will be reached where the signal strength, as observed in the sound reproducing device 20, will be at a maximum, and at this point the system will then be in the superregenerative condition of amplification.

Although in the above method of adjustment of the circuits, it has been indicated that, initially, the variation oscillator is preferably rendered inoperative, there are many conditions of operation under which the incoming signal can be heard only when the circuits are actually amplifying by super-regeneration, and therefore it may be desirable under such conditions to have the variation oscillator always in circuit and operative.

There is thus provided a novel and improved method of obtaining super-regenerative amplifl cation and also novel circuit arrangements and apparatus, whereby the improved method may be carried out and super-regenerative action or amplification obtained more efficiently and effectively than has heretofore been possible,

While several novel circuit arrangements embodying the present invention have been illustrated and described, other changes and modifications which will now appear to those skilled in the art, may be made without departing from the scope of the invention, as for example, the antenna system may be replaced by any suitable source of radio frequency currents which it is desired to amplify, as by wave transmission lines now generally employed. Reference is. therefore to be had to the appended claims for a definition of the limits of the invention.

The herein described invention may be manufactured and used by or for the Government of the United States for governmental purposes Without the payment to me of any royalties thereon.

What isclaimed is:

1. An electric amplification system comprising a regenerative circuit embodying an electron discharge device having an anode, a cathode, a control electrode and an auxiliary electrode and circuits associated therewith, together with means for adjustably and inductively coupling the control electrode circuit and the anode circuit thereof to the point of oscillation, an oscillating circuit, and means inductively coupling said oscillating circuit to said auxiliary electrode for impressing the varying potential of said oscillating circuit on said auxiliary electrode, whereby super-regenerative action is obtained, said last mentioned means including. means oifering a relatively high impedance to the frequencies of the currents to be amplified and relatively low impedance to the varying potentials for substantially eliminating loss of radio frequency energy due to leakage from one circuit to the other.

2. An electric amplification system comprising regenerative circuit embodying an electron discharge device having an anode, a cathode, a control electrode and an auxiliary electrode, said circuit being adjusted near the point of oscillation, a local source of oscillations having a frequency' relatively low as compared to the frequency of the current to be amplified, means inductively coupling said local source of oscillations to said auxiliary electrode for periodically varying the conductance of the auxiliary electrode with respect to the control electrode and the anode to periodically start and stop the oscillations in said regenerative circuit, whereby super-regenerative action is obtained, said coupling means including means for preventing inter-action between the currents to be amplified and the local source of oscillations.

3. An electric amplification system comprising a regenerative circuit embodying an electron discharge device having an anode, a cathode, a control electrode and an auxiliary electrode, said circuit being adjusted near the point of oscillation, a local source of oscillations having a frequency relatively low as compared to the frequency of the current to be amplified, means coupling said local source of oscillations to the auxiliary electrode for impressing an alternating potential on said auxiliary electrode to periodically start and stop the oscillation of said regenerative circuit, whereby super-regenerative action is obtained, and means for maintaining said auxiliary electrode at a normally relatively low potential so that the degree of variation of the alternating potential may be kept within the desired limits required for the most efficient operation of the electron discharge device.

4. An electric amplification system comprising a regenerative circuit including an electron discharge device having an anode, a cathode, a control electrode and an auxiliary electrode, said circuit being adjusted near the point of oscillation, a local source of oscillations of audible frequency, means coupling said local source of oscillations to the auxiliary electrode for impressing an alternating potential on said auxiliary electrode to periodically start and stop the oscillation of said regenerative circuit, whereby super-regenerative action is obtained, a detector circuit coupled to said regenerative circuit for translating the amplified currents into sound vibrations, the coeificient of coupling between the regenerative circuit and the detector circuit being relatively low for audio frequencies so that the amplified currents may be readily transferred from the one circuit to the other while the potentials of audible frequency from the local source of oscillations are prevented from beingtransferred to said detector circuit, whereby an audio hum due to the local source of oscillations is substantially eliminated in the system.

5. An electric signaling system comprising a regenerative circuit for amplifying varying electric currents and embodying an electron discharge device having an anode, a cathode, a control electrode and an auxiliary electrode, said circuit being adjusted near the point of oscillation, a local source of oscillations, means coupling said local source of oscillations to the auxiliary electrode for impressing an alternating potential on said auxiliary electrode 'to periodically start and stop the oscillation of said regenerative circuit, whereby super-regenerative action is obtained, a detector circuit coupled to said regenerative amplifying circuit for translating the amplified currents into sound vibrations, and means for converting said amplifying circuit from a super-regenerative circuit into a regenerative circuit of the tuned radio frequency type, said last mentioned means including a connection from the auxiliary electrode to ground potential and to a source of energy for supplying positive potentials to said auxiliary electrode whereby said auxiliary electrode is grounded with respect to alternating currents of signal energy but is still maintained at a positive static potential.

6. An electric signaling system comprising a regenerative circuit for amplifying varying electric currents and embodying an electron dis charge device having an anode, a cathode, a control electrode and an auxiliary electrode, said circuit being adjusted near the point of oscillation,

a local source of oscillations having a frequency relatively low as compared to the currents to be amplified, means coupling said local source of oscillations to the auxiliary electrode for impressing an alternating potential on said auxiliary electrode to periodically start and stop the oscillation ofsaid regenerative circuit, whereby super-regenerative action is obtained, a detector circuit coupled to said regenerative amplifying circuit for translating the amplified currents into sound vibrations, and means for converting said amplifying circuit from a super-regenerative circuit into a regenerative circuit of the tuned radio frequency type, said last mentioned means including a connection from the auxiliary electrode to ground potential and to a source of energy for supplying positive potentials to said auxiliary electrode whereby said auxiilary electrode is grounded with respect to alternating currents of signal energy but is still maintained at a positive static potential.

7. Anelectric amplification system comprising a regenerative circuit embodying an electron discharge device having an anode, a cathode, a control electrode, and an auxiliary electrode, said circuit being adjusted to a critical point of regeneration, a local source of oscillations, means coupling said local source of oscillations to the auxiliary electrode for impressing a varying potential on said auxiliary electrode independently of the voltage to be amplified to periodically render the regenerative circuit susceptible or insusceptible to be set into free oscillation by the trigger action of the varying electric current to be amplified, whereby super-regenerative action is obtained, and means for maintaining said auxiliary electrode at a normally relatively low potential so that the degree of variation of the potential from the local source may be kept within the desired limits required for the mostefficient operation of the electron discharge device.

8. An electric amplification system comprising a regenerative circuit embodying an electron discharge device having an anode, a cathode, a control electrode and an auxiliary electrode, said circuit being adjusted to a critical point of regeneration, a local source of oscillations having a frequencyrelatively low as compared to the fre-- quency of the current to be amplified, means coupling said local source of oscillations to the auxiliary electrode for impressing an alternating potential on said auxiliary electrode independently of the potential to be amplified to periodically render the regenerative circuit susceptible or insusceptible to be set into free oscillation by the trigger action of the current to be amplified, whereby super-regenerative action is obtained, and means for maintaining said auxiliary electrode at a normally relatively low potential so that the degree of variation of the alternating potential from the local source may be kept within the desired limits required for the most efficient operation of the electron discharge device.

LAWRENCE A. HYLAND. 

